Discussions

Canvas provides an integrated system for class discussions, allowing both instructors and students to start and contribute to as many discussion topics as desired. Discussions allows for interactive communication between two or more people; users can participate in a conversation with an entire class or group.
Discussions can also be created as an assignment for grading purposes (and seamlessly integrated with the Canvas Gradebook), or simply serve as a forum for topical and current events. Discussions can also be created within student groups.
Discussion topics can be organized as focused or threaded discussions. Focused discussions only allow for two levels of nesting, the original post and subsequent replies. Threaded discussions allow for infinite levels of nesting. Focused discussions are relatively short-lived interactions, while threaded discussions allow replies within replies and may last for a longer period of time.

From Canvas Basics Guide > What are Discussions?

LumiNUS equivalent: Forum

Discussions

Use the Discussions Index Page
Create a discussion
Create a group discussion
Duplicate a discussion
Publish or unpublish a discussion
Copy a discussion to another course
Send a discussion to another instructor
Edit a discussion
Delay posting a discussion until a specified date
Move or reorder a discussion
Subscribe to a discussion
Pin a discussion
Close a discussion for comments
Delete a discussion
Enable a podcast feed for a discussion

Discussion replies

Manage student actions

Allow students to:

Create a course discussion
Attach files to a course discussion
Edit and delete their own discussion posts
Like replies in a discussion

Graded discussions

Assign a graded discussion to:
Grade a graded discussion in SpeedGrader

Peer review discussions

Graded discussion via SIS

Set up a graded discussion to be sent to my institution's student information system (SIS) (may not be available in NUS)